1. Field of the Invention
The present invention relates generally to optical components for daylighting and other purposes.
2. Description of Related Art
The term xe2x80x9cdaylightingxe2x80x9d as used in the specification will be understood to refer to applications in which natural daylight is allowed into buildings or other structures (such as vessels or aircraft) through openings provided with means by which the amount of usable light entering through the opening is enhanced by various means. This may be achieved, for example, by diverting light from incident angles at which they would not otherwise provide useful light within the building or other structure, or by capturing light passing the opening which would not otherwise enter the building through it.
A number of previous attempts have been made to improve the daylighting of buildings through transparent elements fitted in openings, such as doors and windows. It was appreciated at an early stage that the provision of a plurality of elementary prism-like structures on one side, or even on both sides, of a pane of glass would provide diversion of incident light utilising the known properties of a prism to refract the light. The benefit of such light-diverting properties lies in the fact that light incident on a window or glazed door from the outside is of greater intensity at high angles of incidence (assuming that the glazing element is planar, lies in a substantially vertical plane, and angles of incidence are measured from the normal or horizontal plane) which means that with traditional plane glazing elements the strongest light arriving from the highest angles passes straight through to illuminate a limited region on the floor of the interior of the building closest to the window, whereas regions further into the room, although they receive light arriving at shallower angles of incidence, are not so strongly illuminated. It is a well-recognised phenomenon that in large rooms lit by a single window in one wall, the level of daylight illumination nearer the back wall and further from the window is less, and frequently considerably less, than the illumination closer to the window.
So-called xe2x80x9cdaylightingxe2x80x9d glazing elements have sought to rectify this situation by diverting light arriving at high angles of incidence, by refraction as it passes through the glazing element, so that the exit angle of at least some of the light arriving from an incident angle above the horizontal is itself above the horizontal so that this light is directed upwards and towards the back of the room instead of being directed downwards to the floor.
Previous attempts to provide daylighting glazing, however, have suffered from the fact that the light-diverting optical properties of the glazing elements have resulted in diffusion of the light into a range of different directions so that an observer within a room has no view through it because light arriving at his eye comes from a wide range of different directions. For this reason, although the daylighting principle is desirable the prior art systems have effectively closed the room from the outside which is a considerable disadvantage from the point of view of the occupants, reducing the daylight to little more than the equivalent of artificial light even though it may have the desirable properties of day light in term of spectral range and colour temperature.
In recognition of this problem a number of element profiles have been developed which are capable, when used in the vertical orientation of traditional glazing, that is with panels lying in a substantially vertical plane, of diverting light incident at high angles above the horizontal and allowing light incident at shallow angles close to the horizontal (both above and below it) to pass through substantially undeviated whereby the occupants of a room can obtain a view through the glazing elements to the outside whilst the high intensity light arriving from high in the sky is diverted towards the back of the room to improve the level of illumination.
The applicant""s own earlier International Applications Nos. PCT/GB94/00949 and PCT/GB97/00517 describe various different profiles using both individual elements and components comprising composite structures, for achieving this desirable effect. One of the profiles utilised comprises what amounts to a parallel series of shaped grooves in one face of an element which, in use, is orientated with the grooves horizontal. The size of the grooves is such that they do not exceed the average pupil diameter of the human eye, but are not so small that diffraction effects predominate, so that the eye effectively integrates the optical effects making it possible to see through the element without significant distortion or interruption of the image.
Of course other applications of the optical component of the present invention are not excluded, and its description with reference to daylighting purposes is to be understood as being without prejudice to the generality of the invention. In particular, the optical component of the present invention may be utilised as a cover for a light source where it may be desired to divert light generated thereby or for any of a range of other applications in which optical components may be used, such as in the illumination of screens (both those bearing images and those acting as barriers) transmission of images and/or illumination of advertising signs, shop windows or the like. When diverting light by the use of refraction and/or reflection one problem which continually arises is that of chromatic dispersion which can be of significance especially if the diverted light is to be used for imaging purposes. Another problem arising with daylighting elements generally, is the possibility of glare arising from, for example, the region immediately around the sun, which is usually out of the normal line of vision but which, because of the diversion of incident light, may have an apparent direction which impinged detrimentally on the field of view of occupants within the building. Brightness variations from day-to-day can also mean that a daylighting system which works well for average conditions is inadequate in dull or overcast conditions and excessively or uncomfortably bright in clear-sky conditions.
The present invention seeks to provide means by which these disadvantages of daylighting systems can be mitigated at least to some extent, and to provide configurations of daylighting elements and components which will improve the performance of daylighting systems generally and extend the range of applications to which they can be put. The present invention also seeks to introduce further ideas and concepts about how optical elements can be adapted to enhance the internal illumination of buildings.
According to one aspect of the present invention, therefore, an optical element of the type comprising two optically transparent bodies each having two major faces one of which is interrupted by a plurality of cavities separating the said major face into a plurality of first elementary surfaces, between the cavities there being cavity separators defined by second elementary surfaces at which light incident through the corresponding optically transparent body above a certain threshold angle is reflected by total internal reflection and below which threshold it is transmitted and refracted, in which the shape of the cavities of the two bodies is complementary and such that the cavity separators between the cavities of one optically transparent body and the cavities of the other optically transparent body interpenetrate one another such as to define, for each cavity, at least two voids between facing elementary surfaces at which total internal reflection takes place.
In embodiments of the present invention the interpenetrated bodies may be in the form of substantially flat panels positioned face-to-face and these bodies may be sufficiently rigid to be self-supporting, or may be formed as thin films to be carried on other transparent supports such as the plane glass of conventional window glazing.
Earlier optical components involving two interpenetrating bodies have been so shaped that there is only one void defined by each pair of interpenetrating cavity and cavity separator. The present invention thus provides twice as many potential reflector sites for a given cavity structure as the prior art.
The present invention also comprehends an optical component as defined above in which the cavities are defined by elementary surfaces and at least two of the elementary surfaces defining a cavity are substantially parallel to one another, the distance between two such parallel elementary surfaces through a cavity separator being less than the corresponding distance within a cavity where by to allow inter penetration of cavity separators and cavities and formation of the said two voids per cavity.
The elementary surfaces defining a given cavity may be inclined with respect to a normal to the major faces of the component or may be parallel to such normal. In the former case the inclination may be alternately in opposite directions such that each cavity is slightly tapered towards the interior of the body (that is the cavity is slightly flared) which if the optically transparent body is produced by moulding aids mould release and furthermore assists interpenetration upon assembly of the two bodies to form the component.
In a preferred embodiment of the invention the elementary surfaces delimiting each cavity define both side walls and bottom walls of the cavity, and in this case it is preferred that the said at least one major face of the optically transparent body is separated by the cavities into first elementary surfaces which have a form and inclination matching that of the said bottom walls whereby to mate closely therewith when the two bodies are placed together with their cavities and cavity separators interpenetrating.
The profile shapes of the two bodies, that is the cross-sectional shape of the cavities and cavity separators may be identical. In such a case the bodies may be made with the use of a single mould and simply inverted with respect to one another in order to position them for interpenetration of their cavities and cavity separators.
The cavities may be of any form in which surface elements (preferably but not necessarily planar surface elements) define appropriate regular or irregular polygonal outlines. For example, the cavities may be triangular, square or hexagonal in plan form with the cavity separators being correspondingly shaped. In a preferred embodiment, however, the cavities are in the form of elongate grooves and the cavity separators are in the form of elongate ribs. The elementary surfaces defining the side and/or bottom walls of a cavity may be so shaped as to reduce or eliminate the incidence of light approaching at certain angles. This may be achieved, for example, by the shape of the cavity side and/or bottom walls. This shape may, for example, be such that the voids formed bet ween the walls upon interpenetration of the two bodies taper to a point in cross-section (that is a line in three dimensions in the case of elongate grooves) which result in light incident at a particular angle not reflected at the interface defined by the side walls is suppressed and prevented from passing through to form light beams in unwanted directions.
Preferably at least part of at least some of the cavity side and/or bottom walls are surface treated and/or coated whereby to inhibit the transmission of light through the component from a limited range of incident angles.
Embodiments of the present invention may be formed in which at least some of the surface elements defining the side and/or bottom wall of the cavities contact one another when the bodies are positioned interpenetrating one another, in such cases there may further be provided a transparent or translucent interstitial material having a refractive index not less than that of the body on the incident side of the interface thus defined and not greater than that of the body on the exit side of the interface thus defined. This, of course, implies that the two bodies have a different refractive index from one another although the case in which both bodies have the same refractive index and the interstitial material has the same refractive index as the bodies is not excluded.
Conveniently the transparent or translucent interstitial material may be an adhesive. Such a configuration ensures that light contacting the interface at or near grazing incidence, which can occur at inclined interfaces in optical components of the type defines herein, is not reflected.
The choice of orientation angle of the interface and the interstitial materials in particular the refractive index of the material, allows control to be exerted at the design stage on the angle of incidence of light, with respect to the major faces of the component, at which occurs the transition from reflection through the interface to reflection at it. This design choice allows the designer to prevent the transmission of unwanted light from a certain range of elevation angles while permitting the transmission of light from other angles. This may typically be exploited as a sun shading function which operates over only a small range of elevation angles, for example centred on the average position of the sun. In such a way the view through the component, an important factor in all the embodiments of the present invention, is suppressed at or near the elevation of the sun whilst normal viewing through the element is afforded in all other directions. This can be achieved, of course, without detriment to the interior illumination and particularly the enhancement in what would be provided by alternative shading means such as conventional blinds.
The present invention thus comprehends an optical component of the type comprising optically transparent bodies having major faces at least one of which is interrupted by a plurality of cavities with cavity separators between them, formed as a sun shade or barrier to prevent the transmission of light through the component from certain incident angles or ranges of angles. This can be achieved by a combination of the choice of orientation angle of an interface and refractive index of interstitial material between the surfaces defining the interface whereby to determine the angle of incidence at which the transition from refraction through the interface to refraction therefrom occurs.
In order to control chromatic dispersion the optical component of the present invention is provided with interfaces within a limited range of angles. In particular the angle of inclination of those surface elements of the bodies which define interfaces at which reflection takes place preferably lie at an angle to the normal to the major face of the body which does not exceed 7xc2x0. In fact, it is more preferable for the angle of such interfaces to be limited to not more than 5xc2x0. Embodiments of the present invention may also be provided in which the surface elements are configured to allow the use of the component as a mirror.
The above discussion is based on the assumption that the optical elements forming the two bodies from which the component is assembled, lie with their major faces parallel to the plane of an opening. Other embodiments, incorporating components which do not span the entirety of an opening, are possible as will be discussed below. In one such arrangement an optical assembly including optical components as defined hereinabove, in which the transparent bodies are sufficiently rigid as to be self-supporting or are carried on a or a respective transparent or translucent support, is so formed that the bodies and/or the supports are elongate and held in an array substantially parallel to one another. In one embodiment such an array is comparable in configuration as to that of a Venetian blind with the slats lying horizontally or vertically.
If the cavities in the transparent bodies are elongate grooves these may lie either parallel to the length of the slats or perpendicular thereto, or may be inclined with respect to their length. Likewise, the slats themselves may be inclined with respect to the horizontal (in order to lie as closely as possible to the path of the sun) and the slats may be fixed or adjustable in inclination about an axis parallel to the lengths of the slats. Such adjustment may be effected manually or there may be provided means for automatically adjusting the inclination of the slats about their respective longitudinal axis in dependence on a signal from a light sensor representing the incident direction of the major part of the incident light.
The present invention also comprehends an array of elongate bodies and/or supports in the form of a substantially planar array pivotally mounted or mountable outside an opening in a building or the like in such a way that the array can turn as a whole about a pivot axis parallel to one edge thereof. In configurations such as that described above, in which the bodies or supports are in the form of slats of a venetian blind, these may or may not be individually turnable about their own respective longitudinal axis.
The array of elongate bodies and/or supports may be mounted or mountable outside an opening in the building or the like without being turnable about one edge, but with the plane of the array being inclined with respect to the plane of the opening whereby to intercept light travelling downwardly past the opening, the reflecting interfaces of the optical components being oriented such as to divert this downwardly-directed light through the opening.
The present invention also comprehends an optical assembly comprising at least one optical component of the type comprising two optically transparent bodies each having two major faces at least one of which is interrupted by a plurality of cavities with cavity separators between them, the two bodies being positioned with their said one major faces in contact and the cavities and cavity separators interpenetrating one another to form a plurality of closed voids, in the form of a panel having means for supporting the panel over the outside of a window or other opening in a building or the like with its plane inclined to the vertical whereby to divert into the opening light travelling downwardly past the opening. Such a panel may be mounted in such a way that its inclination is adjustable.
The present invention also comprehends an optical assembly comprising at least one optical component as herein defined, in the form of a glazing panel in or over a window or like opening in a building, together with a further light-diverting component within the interior of the building and positioned in the path of light diverted by the said optical component and acting to divert the light incident on it. The said further light-diverting component may be a curved or plane reflector. In the former case the curvature may be cylindrical or spherical.
In any daylighting system of the present invention there may also be provided an additional artificial light source and means for positioning the source outside an opening in a building and orienting it in such a way as to direct light towards the opening. In an assembly of this type the light-diverting optical component may be so designed that light projected by the artificial light source is diverted by the optical component in a predetermined direction or range of directions. The present invention also encompasses an optical component of the type comprising two optically transparent bodies each having two major faces one of which is interrupted by a plurality of cavities separated by cavity separators, positioned in face-to-face relation with the cavities and cavity separators of the two bodies interpenetrating one another, with an air gap between them, in which the cavities and cavity separators are so shaped as to define in the assembled component substantially catadioptric reflectors at least for light incident over a certain range of incident angles.
In one embodiment the said one major face of each body is interrupted by elongate grooves defined by inclined planar faces. In such an embodiment the two inclined planar faces defining the grooves are preferably inclined at substantially 90xc2x0 to one another.
An optical assembly comprising a set of optical components having catadioptric reflectors as discussed above may be formed with the components as elongate strips or slats the inclination of which about an axis parallel to their length is adjustable.
Another function which can be fulfilled by optical components formed in accordance with the present invention is that of limiting the direction of transmission of light incident over a range of directions. This may be of value, for example, if the optical component is a screen over a light source or, for example an instrument panel or the like in preventing unwanted transmission of light in certain directions.
Typically a screen over an instrument panel may limit the transmission of light to a narrow band of angles to either side of a normal so that only a user positioned directly in front of the instrument can read it and observers to the side of the instrument, outside the range of transmission angles, receive no light and therefore no image. The restrictions on transmitted light may also of course apply to reflected light so that embodiments of the invention may be used to reduce unwanted reflections (particularly at night), or to reduce glare or improve display contrast. This may be of value in a wide range of applications where a user may wish to observe an instrument panel, such as a motor vehicle or aircraft instrument panel, without disturbing reflections from nearby light sources.
According to another aspect of the present invention, therefore, there is provided an optical component of the type comprising two or more optically transparent bodies each having two opposite major faces one of which is interrupted by a plurality of cavities, defined by elementary surfaces, with cavity separators between them, in which the two bodies are engaged in face-to-face relationship with their said one faces in contact such that the cavity separators of one body penetrate into the cavities of the other, the shape of the cavities being such that at least one elementary surface thereof is not contacted by the corresponding elementary surface of the cavity separator of the other body when the two bodies are fully engaged whereby to form a void between them, the void containing a non-transparent material.
The said one elementary surfaces defining the voids may be of a variety of shape and configuration. In a first embodiment the said one elementary surfaces are flat at least over the major part of their area and lie substantially orthogonal to the said major face of the optically transparent body. In such an embodiment incident light normal to the component is transmitted through it substantially undeviated, as is light incident at a range of angles from the normal up to a certain threshold angle determined by the ratio between the spacing of the cavities and their depth. Light incident at greater angles is absorbed at the interfaces between the material of the bodies and the non-transparent material in the cavities.
A preferential direction of transmission can be provided if the said one elementary surfaces forming the voids lie at an angle to the normal such that the range of incident angles transmitted through the component is inclined as a whole to the normal. This may be relevant, for example, for use as cover panel to an instrument which is located some distance to one side of an observer.
The nature of the non-transparent material in the voids may be chosen to achieve a desired effect. By selecting a material having a refractive index less than that of the bodies, and by using as the non-transparent material one which is translucent or at least not entirely opaque, it is possible to have at least part of the incident light at certain angles reflected, as well as some of the light incident at other angles being absorbed whilst incident light within the said transmission range of incident angles is transmitted. Such an embodiment may be used for interior lighting as well as for displays, or for daylighting purposes where glare at certain incident angles is a problem which can be overcome by absorbing the incident light at those angles.
The practical construction of such embodiments of the invention may be achieved in a number of ways. For example a non-transparent adhesive may be coated on to one or both facing major surfaces of the two bodies before they are brought together. By applying a sufficiently great pressure to the two bodies the adhesive between the elementary surfaces of the cavities and cavity separators which are in direct contact with one another is effectively squeezed out so that these faces are not spaced by a film of adhesive. The adhesive squeezed out from between the contacting elementary surfaces fills the voids between the said one (non-contacting) elementary surfaces to form, in the finished product, an array of elementary opaque elements acting to absorb light incident thereon.